update docker-py test status code from 500 to 400

Signed-off-by: allencloud <allen.sun@daocloud.io>

Author: allencloud

tests/integration/api_swarm_test.py

@@ -168,7 +168,7 @@ def test_remove_main_node(self):
         with pytest.raises(docker.errors.APIError) as e:
             self.client.remove_node(node_id)
 
-        assert e.value.response.status_code == 500
+        assert e.value.response.status_code >= 400
 
         with pytest.raises(docker.errors.APIError) as e:
             self.client.remove_node(node_id, True)